How i can subtract a point on an elliptic curve?

Sanka555

member

Activity: 96

Merit: 36

Thank you very much this is exactly what I need

MixMAx123

full member

Activity: 161

Merit: 168

Yes:
https://github.com/MrMaxweII/Secp256k1

Code:

import java.math.BigInteger;
import ECDSA.Secp256k1;

public class Test 
{
	public static void main(String[] args)
	{
		BigInteger[] p1 = new BigInteger[2];
		BigInteger[] p2 = new BigInteger[2];
		p1[0] = new BigInteger("af7ea2a1270f6630251eed5a3e2dd036f97c340b0a44589a8c4da9bb1386716",16);
		p1[1] = new BigInteger("5ed9fd31f92fec4b511d1667a6174c851bf8dc536538aeb8c1055b8be7b2add7",16);
		p2[0] = new BigInteger("c57e3b2c8edb3032a634700069220a4be1535668978844d271349298310dc2a1",16);
		p2[1] = new BigInteger("a81df44f0d3cea24b7b021b0708a9fdcb1fce6e4e5c98348efe84624364e37d6",16);		
		BigInteger[] p3 = Secp256k1.subtraktion(p1, p2);
		System.out.println(p3[0].toString(16));
		System.out.println(p3[1].toString(16));
	}
}

Output:

Code:

7eb33c2cdaa4868b6187b467d09e35e7a33db8ab6c74f1fc54ba22cb8ea0834d
e58ea47bb4be30c6a3696e8d74b82187e0baa5649b2a3303e30a900c855a6940

Sanka555

member

Activity: 96

Merit: 36

are there any Java libraries that allow you to subtract a point on an elliptic curve

I found python, but maybe there is a ready-made Java library so as not to rebuild the bike?)
Thank you very much in advance

Quote

# -*- coding: utf-8 -*-

def OnCurve(x,y): # Check if the point is on the curve
   A = (y*y)%P
   B = (x*x*x)%P
   C = False
   if A == (B + 7):
   C = True
   return C

def ECadd(xp,yp,xq,yq): # EC point addition
   m = ((yq-yp) * modinv(xq-xp,P))%P
   xr = (m*m-xp-xq)%P
   yr = (m*(xp-xr)-yp)%P
   return (xr,yr)

def legendre_symbol(a,p):
   ls = pow(a, (p - 1) / 2, p)
   return -1 if ls == p - 1 else ls

def modsqrt(a,p):
   if legendre_symbol(a, p) != 1:
   return 0
   elif a == 0:
   return 0
   elif p == 2:
   return p
   elif p % 4 == 3:
   return pow(a, (p + 1) / 4, p)
   s = p - 1
   e = 0
   while s % 2 == 0:
   s /= 2
   e += 1
   n = 2
   while legendre_symbol(n, p) != -1:
   n += 1
   x = pow(a, (s + 1) / 2, p)
   b = pow(a, s, p)
   g = pow(n, s, p)
   r = e
   while True:
   t = b
   m = 0
   for m in xrange(r):
   if t == 1:
   break
   t = pow(t, 2, p)
   if m == 0:
   return x
   gs = pow(g, 2 ** (r - m - 1), p)
   g = (gs * gs) % p
   x = (x * gs) % p
   b = (b * g) % p
   r = m

def modinv(a,n): # Extended Euclidean Algorithm in elliptic curves
   lm, hm = 1,0
   low, high = a%n,n
   while low > 1:
   ratio = high/low
   nm = hm - lm * ratio
   new = high - low * ratio
   hm = lm
   high = low
   lm = nm
   low = new
   return lm % n

def ECadd(xp,yp,xq,yq): # EC point addition
   m = ((yq-yp) * modinv(xq-xp,P))%P
   xr = (m*m-xp-xq)%P
   yr = (m*(xp-xr)-yp)%P
   return (xr,yr)

def ECsub(xp,yp,xq,yq): # EC point subtraction
   X = (((yp+yq)*modinv(xq-xp,P))**2-xp-xq)%P
   A = (xp + X + xq)%P
   B = modsqrt(A,P)
   B1 = P - B
   Y = yq - (xq - X) * B
   X = X % P
   Y = Y % P
   if not OnCurve(X,Y):
   Y = yq - (xq - X) * B1
   Y = Y % P
   return X,Y

P = 2**256 - 2**32 - 2**9 - 2**8 - 2**7 - 2**6 - 2**4 - 1

Gx = 55066263022277343669578718895168534326250603453777594175500187360389116729240
Gy = 32670510020758816978083085130507043184471273380659243275938904335757337482424

print Gx,Gy

Ax,Ay = ECadd(Gx,Gy,Gx,Gy)
print Ax,Ay

Bx,By = ECsub(Ax,Ay,Gx,Gy)
print Bx,By
This code is from here.

It works perfect in Python 2.7.13.

Topic: How i can subtract a point on an elliptic curve? (Read 150 times)